Imaging systems, such as digital cameras, satellites, and image scanners, operate by converting electromagnetic energy from a source image to an electronic, i.e., digital, representation, of an image. The source image could be an actual view, such as a landscape, satellite image, and the like, or embodied in a physical form, such as a photograph, film, picture, document, and the like. In many applications, the electromagnetic energy used to convert the image into a digitized image is visible light, however, infrared, microwave, and other suitable types of electromagnetic energy are also be used to create the digitized image.
Imaging systems generally include a number of optic sensors. The sensors measure the intensity of electromagnetic energy within a specific bandwidth of the electromagnetic spectrum. Each sensor generally comprises a color filter and a photodetector, such as a charge-coupled device, phototransistor, photoresistor, and the like. The photodetector produces an electrical signal that is proportional to the intensity of electromagnetic energy striking the photodetector. The color filter blocks all wavelengths of light in the visible electromagnetic spectrum except a specific bandwidth. For example, in a red sensor a red filter blocks all other wavelengths of light in the visible spectrum except for the wavelengths of light associated with the color red. Accordingly, only the red bandwidth of light from the source image is measured by the red sensor.
The sensors are generally geometrically positioned in arrays such that the electromagnetic energy striking each sensor corresponds to a distinct location in the source image. Accordingly, each distinct location of the source image corresponds to a distinct location, or pixel, in the digitized image. In color applications, the electronic imager comprises an array of color optic sensors relating to one of the three primary colors—red, green, and blue. The intensity of red, green, and blue electromagnetic energy associated with each discrete location of the source image is measured and recorded.
In electronic scanner applications, the scanner records the color intensity for each color optic sensor in a sequence of scan positions until the entire image is scanned. The spacing between scan positions is referred to as the scan line pitch. The scan line pitch is generally the same as the pixel pitch, i.e., width of the line of detectors, but may vary depending on the desired image resolution. The color data relating to each pixel is then correlated to produce the digitized image.
The digitized image often includes imperfections that are not present in the source image. One cause of such defects is the optical components of the imaging system. For example, in the case of a electronic imagers, the scanning surface or “platen” in the electronic imager may contain scratches and other optical path obstructions. Dust, fingerprints, and other such debris also causes optical path obstructions. These optical path obstructions are digitized along with the real image and appear as imperfections in the digitized image.
Another cause of imperfections is defects within the physical medium of the source image. For example, a photograph, film, or other physical medium having an image thereon may be scratched, distressed, or deformed despite careful handling. In addition, imperfections may arise from foreign matter, such as a hair, dust, and the like being deposited on the physical medium while the image is digitized. Thus, even though an image is replicated exactly as contained in the physical medium, imperfections may still be present in the digitized image.
One method of removing imperfections from transparent physical mediums, such as film, is to transmit infrared (IR) light through the transparent medium to produce a defect image. Conventional electronic imagers use the red filtered photodetector or a dedicated infrared photodetector for detecting and measuring the infrared light. As a result, conventional electronic imagers require two complete scans of the source image. The first scan uses conventional light to create a color digitized image. The second scan uses infrared light to create a digitized defect image that is used to correct the defects in the digitized image. A disadvantage of conventional methods is that the infrared scan takes the same length of time to complete as the color scan. Accordingly, this method for defect correction doubles the duration of the scanning process.